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Passive House (Passivhaus) in the Northwest May 29 2009

I have just completed the first of three 3-day sessions of the Passive House Consultant Training. It was a compelling introduction to the principles and techniques of this approach to radically reducing the energy used in buildings--to the point that the house can be heated with the equivalent of a hair dryer! We are going to use this approach with two of our current projects, and hope to incorporate this into all of our projects going forward. Here are a few highlights:

• Typically when we design energy-efficient houses, we start with our more or less standard (to us) approach to the envelope of the house, and then size the mechanical system to suit the heat loss of the envelope. With Passive House approach, it's the other way around: we start with a fixed amount of energy that can be used for heating, cooling, lighting and plug loads (4.75 kBtu/SF/year), and design the envelope to make that work.

• Insulation varies with the climate, but in Seattle will likely be in the range of R-60 for walls, ceilings and slabs. Walls will be about a foot thick, offering lots of potential for design of the exteriors.

• The detailing of the ways wall, floor and slab meet each other will be different, primarily to eliminate thermal bridges.

• The houses will be very tightly constructed. Air infiltration and leakage will be less than 0.6 ACH@50 (air changes per hour at 50 Pascals. Typical construction is the range of five or six ACH@50.

• In the heating season, lots of fresh air will be supplied by a heat recovery ventilator.

• Windows and doors with a U-value of 0.09 will probably be imported from Germany. There are currently no manufacturers in the United States making windows or doors that qualify, though Serious Windows does come close.

• We will optimize passive-solar and internal heat gains. At this level of efficiency, the warmth generated by the refrigerator (and other appliances) must be accounted for! This also means careful study of shading, to prevent over-heating. Interestingly, the Passive House will not have a huge bank of south-facing windows, and no windows elsewhere, like the stereotypical "passive solar" house.

• We will be modeling the energy gains and losses using a program called the Passive House Planning Package, a sophisticated Excel-based spreadsheet.

• Sometimes referred to with its German spelling, Passivhaus, to distinguish it from "passive solar" houses.

• Inspired by work in the United States, but developed in Germany. So far there are only a dozen or so Passive Houses built in the US, but over 10,000 in Europe.

More on this later!

RH